Equipoising support apparatus

ABSTRACT

A force exerting device having a force exerting structure including a load arm as a first side, pivotable about a load pivot, a resilient member attached to the load arm and to a termination point and forming a second side of the force exerting structure. The third side of the structure is formed by a line from the termination point to the load pivot. A first adjustment mechanism moves the termination point to change the length of the third side of the structure. A second adjustment mechanism moves the termination point in a direction different than the first adjustment direction so the termination point location can cross a substantially plumb line passing through the load pivot. A force modification device may be included to dynamically adjust the resilient member termination point position in response to motion of the load arm.

This application is based on, and claims priority to, provisionalapplication Ser. No. 60/672,186, having a filing date of Apr. 15, 2005,and entitled, Auto Adjusting Equipoising Support Apparatus.

BACKGROUND OF THE INVENTION

This invention relates generally to equipment supports, and moreparticularly to portable equipment utilized in conjunction with motionpicture or video cameras.

Mobile film or video cameras typically require angular and spatialstability in order to obtain smooth, high-quality results. TheSteadicam® portable camera stabilizing device, which has become a defacto standard in the TV and movie industry, was developed to permitstable ambulatory videography or cinematography by an operator. Theinventor's U.S. Pat. No. 4,017,168 (Re. 32,213), U.S. Pat. Nos.4,156,512 & 4,474,439 are directed to aspects of such stabilizingdevices.

Spring powered ‘equipoising’ parallelogram arms have been used fordecades to support and position payloads such as lamps, x-ray machinesand dental equipment. These arms rely to a greater or lesser extent onfriction to retain a set angle or position, since existing springgeometries do not necessarily provide appropriate or consistent liftthroughout the entire angular excursion of the parallelogram links. TheSteadicam®, however, provides near frictionless support of the floatingcamera payload in order to isolate a camera from unwanted spatialmovements of the operator, and further mandates a spring design for thesupport arm that will equipoise almost perfectly, that counters thefixed weight of the gimbaled camera assembly with nearly constantpositive buoyancy from its lowest to its highest point of parallelogramexcursion

The formulas for determining the appropriate spring rate to achieve thisin equipoising arms factor down to the expression K=P/d, where K is thespring rate, P is the load and d is the height of the lifting triangle,which is incorporated into the parallelogram and exercises it upward.When a spring of the rate specified in the above formula is deployed asa side of the triangle, it produces the appropriate force to exactlylift the specified weight throughout the entire vertical range ofmotion. This property is termed “iso-elasticity”.

It is noted that any shaped lifting structure can be used that followsthe principals described herein and can be substituted for the “liftingtriangle” referenced extensively throughout. It is also noted thatreference to a triangle or structure sides does not necessarily mean thesides are physical structures.

In order to lift the load consistently throughout the entire excursionof the typical parallelogram arm, however, spring rate indicated by theabove formula mandates spring designs that are typically up to threetimes as long as the diagonals across which they are to act. The presentinventor's U.S. Pat. Nos. 4,208,028 and 4,394,075 originally solved thisproblem by dividing the spring into a chain of three spring segments inseries, interconnected by steel cables running over pulleys at theparallelogram link ends, that permitted the entire spring to expand andcontract, and yet still applied the sum of the collective force inseries across the diagonal, as if produced by a single, continuousspring.

In practice it was found that when the support of lighter camerasrequired relaxing the tension of the spring series, the spring ratebecame inappropriate for those reduced loads and iso-elasticity wascompromised. As a consequence, the arm tended to ‘ride’ harshly and thedesired positive buoyancy for the load only prevailed in one sector ofits vertical excursion. Further, this three-spring solution was complexand expensive, requiring a plurality of pulleys and robust cables.

The present inventor's U.S. Pat. No. 5,360,196 (the '196 patent)describes an arm that is powered by a single, high-rate spring, applyingits force via a differential pulley and tackle through a cable runningacross the diagonal, so that the effective rate is appropriate foriso-elasticity according to the above formula. This arm adjusts thelifting strength of the arm in a novel manner by raising and loweringthe attachment point of the spring cable within the parallelogramlinkage (thus increasing or decreasing the height, and thus theefficiency, of the lifting triangle) without compromising the springrate required to provide ‘iso-elasticity’. The same formula, K=P/d,indicates that if only the height of the appropriate lifting triangle isincreased or reduced proportionately with the weight to be carried, theproperty of iso-elasticity will be maintained. In practice, the armembodying the technology claimed in the '196 patent was found to besomewhat frictional due to the ‘gear ratio’ of the differential pulley.Also, the closer iso-elasticity was achieved, the more erratic was thearm's behavior at the extremes of high and low lifting position. As thelifted or depressed angle of an equipoising support arm exceeds 50° fromthe horizontal, its exact performance is increasingly subject to minutevariations of load, torque, friction and the collective bearingtolerances of its pivots.

The present inventor's continuation of the above patent, U.S. Pat. No.5,435,515 (the '515 patent), reverted to the complex and expensive‘three-spring’ method to achieve iso-elasticity, but sought to achievepredictable performance at the high and low extremes of excursion byselectably decreasing the lifting efficiency of the spring geometry.This was done by adjustably offsetting the path of spring termination sothat it was raised and lowered along a line within the parallelogramthat was angularly displaced from vertical in order to slightly reducethe degree of iso-elasticity. The angle of the line was fixed, however,and since only its lateral displacement could be adjusted, its effectinappropriately increased rather than decreased the lifting efficiencywhere it was most needed—as the spring termination point was lowered.

What was needed was a means that would permit the use of a single springthat could actually fit within the diagonal distance of a support armparallelogram and still produce iso-elastic equipoising of the load. Anarm was also needed that would predictably, frictionlessly, equipoisethe load throughout its entire excursion—all the way from its lowest toits highest parallelogram positions.

All previous Steadicam®-type arms, particularly those that approachiso-elasticity under certain loads, have needed to arbitrarily restraintheir vertical travel to a degree of parallelogram excursion well shortof maximum or minimum in order to avoid unruly, unpredictableperformance at extreme high and low angles. Even with a degree ofcontrol over iso-elasticity, parallelogram arms were still prone tounexpected and forcible closure as angles neared 60° above or belowhorizontal. Arms would typically be characterized as those that‘behaved’ and those that arbitrarily ‘locked up’ at those high and/orlow excursions.

Restraining ‘bumpers’ have, therefore, been a feature of theseequipoising arms from the beginning. The more ‘iso-elastic’ the springgeometry, the more irregularly the arms tend to lift at these verticalextremes of excursion. This is partly a consequence of the unpredictablyvarying torques imposed by the cantilevered, gimbaled payloads that hangat various angular positions relative to the arm parallelogram. Theresult has been an uncontrollable tendency to lock up, or lurch‘over-centers’, at the high or low position, and so various bumperdesigns have, in some cases, restrained the travel to as little as 45°above level. In no case were the angular extremes of lift available fromsuch parallelograms, and thus the lifting range of travel of the armswas curtailed. In addition, bumpers “bumped” more or less suddenly andfurther caused operators to be wary of approaching them—which furtherlimited the usefulness of these support arms. What was needed waspractical control of the general level of iso-elasticity, and further,some additional automatic control over the geometrical contour of liftthat would provide smooth, predictable behavior at these extremehigh-low angles of arm excursion, by gently de-powering the arms justbefore bumping, clunking or shooting over centers and locking up.

Applicant has previously refined the ‘offset’ concept described in the'515 patent, and placed it fixedly ‘outside’ vertical to, in effect,uniformly change the effective rate throughout the arm's excursion andsimulate the effect of the correct rate using a spring short enough tofit into the diagonal (this concept has been successfully marketed asthe ‘Flyer’ arm). Limitations in the Flyer arm, however, were evident atextremes of high lift. There was also an irregular curve of performance.

Parallelograms are capable of closing to nearly ±80°, but havepreviously been unusable at those angles due to the foregoing problems,despite various bumper schemes employed to tame these extreme up/downpositions.

What is further needed is a way to regularize and level out the liftingcurve and avoid the tendency to jump ‘over centers’ and lock up athigh/low extremes.

SUMMARY OF THE INVENTION

The present invention is directed to the field of parallelogramequipoising support arms for camera stabilizing devices. Illustrativeembodiments of the invention comprise a tensioning assembly that canprovide two different fixed adjustments and one automatic, preferablyeccentric, adjustment to the geometric relationship between the endpoint of the tensioning assembly and the remaining structures thatcomprise the support arm, in order to provide a consistent lifting forceby means of a resilient member of appropriate dimension but notnecessarily appropriate ‘spring rate’. The adjustments can includealtering the elevation of the tensioning assembly termination and/or itslateral relationship with reference to the structure. The automaticadjustment can include cyclical further alteration of the lateralrelationship in response to movement of the parallelogram through itsexcursion.

In a first, aspect of an illustrative embodiment of the invention, aforce-exerting and/or lifting triangle, which provides the lifting powerfor the support arm, comprises a long side and a short side pivotallyconnected at a variable angle, with a resilient member pivotally forminganother side of the triangle so as to bias the angle appropriately forthe purpose of equipoising the payload. The efficiency of the liftingtriangle can be improved in two ways: 1) by pivoting the short side ofthe lifting triangle to a optimal offset angle with reference tovertical and 2) by an additional, dynamic angular alteration of theverticality in response to the raising or lowering of the long side ofthe lifting triangle.

Another exemplary embodiment of the invention provides for selectablyraising and lowering the terminal points of the resilient member alongthe line of the pivoting short side of the lifting triangle in order toincrease or decrease the load that is equipoised. The length of thepivotable short side will thus be lengthened or shortened progressivelyalong the angle that is the sum resulting from adjustments 1 and 2above.

A further illustrative embodiment of the invention provides for thearcuate adjustment of the short side in reference to a plumb linethrough the apex of the triangle, so as to alter the effective rate, andthus the lifting efficiency, of the resilient member in order to liftconsistently, even though the resilient member may be of aninappropriate spring rate.

A further illustrative embodiment of the invention, includes an arcuateadjustment that is additionally dynamically varied with reference to theplumb line by cams or linkages directly or indirectly actuated inreference to the pivoting of the long side of the triangle at the apex.

In a particular illustrative embodiment of the invention, alternativelythe magnitude of the additional dynamic adjustment is controlled byeither a selection of more or less circular cam sizes and shapescentered on a point fixedly or adjustably referenced to the long side ofthe lifting triangle. The amount of adjustment and the arm excursionposition in which the adjustment takes place will be dependent primarilyon the shape of the cam and the placement of the pivot point.

In a further embodiment of the invention, the magnitude of theadditional dynamic adjustment is controlled by a crankshaft pivoting ona point fixedly or adjustably associated with the long side of thelifting triangle.

In a further embodiment of the invention the magnitude of the additionaldynamic adjustment is controlled by a turnbuckle of selectable lengthpivoting on a point fixedly or adjustably associated with the long sideof the lifting triangle.

In a further embodiment of the invention, chambered extrusions areemployed to form parallelogram links and end-blocks to provide maximumtorsional stiffness with the lightest possible weight.

In a further embodiment of the invention, the provision of a novelturnbuckle design provides for the pivots to be closer together thanpossible with conventional turnbuckles and the adjusting knob to bedisplaced away from the line between the pivots, and thus out of the wayof the end block as employed in embodiments of the present invention.

Embodiments of the invention provide ways to actively adjust the springoffset relative to the parallelogram position so that the lift isselectably appropriate throughout the range. Therefore, the simplest ofbumpers at approximately ±70° range are sufficient to restrain and tamethese most extreme excursions. (Previous arms have limited the range toas little as 55° to avoid this problem, which has caused a severereduction in the lifting excursion, and thus of the usefulness of thearm to mimic the entire lifting range of the human arm (alongside whichthese arms operate), in order to relieve the operator of the weight ofhis or her equipment.

In an illustrative embodiment, the active adjustment of the springoffset is performed with a crank pivot axle approximately in line with atransverse link of the parallelogram and external to its adjacent pivot;and a crank arm, pivoting on the axle, that swings the bearing shafttoward and away from the interior of the parallelogram, but generallyoutside of the vertical line between the adjacent end pivots, so thatthe lifting efficiency of the resilient member is dynamically altered inresponse to the momentary angle of the parallelogram arm, from lowest tohighest.

The crank can be a turnbuckle which provides combined iso-elasticity andlifting curve adjustment, simultaneously adjusting the springtermination offset and the aggressiveness of the cam effect for the‘active contouring’ of the lifting force so that it is not excessive athigh angles (which would lock up the arm) and not insufficient at lowangles (which would likewise impel it ‘over centers’ and into a lockedup condition).

Embodiments of the invention are directed to a lifting triangleoperating in conjunction with a parallelogram support arm and comprisinga substantially vertical shorter side, a longer side and another sidethat consists of a flexible, resilient member, the expansion orcontraction of which pivotally biases the apex angle of the sides (andthus the associated parallelogram) from its most obtuse form, up pastthe condition of being a right angle and on up to its most acute form.

The long side of the lifting triangle can be contiguous with one of, orparallel to, the long sides of the parallelogram,

The angle of the short side is preferably variably fixed in angularreference to the adjacent, roughly vertical, leg of the parallelogram(with reference to a plumb line that passes through the apex of thetriangle), such that the degree of iso-elasticity is nominallyacceptable, even though the selected rate of the resilient member doesnot conform to the K=P/d formula for the iso-elasticity.

The angle of the ‘short’ leg with reference to vertical may beadditionally, actively controlled, by means of cams, crankshaft linkagesor the like, as the parallelogram arm is biased by the flexibleresilient member. The dynamic control varies the position of thetermination point of the resilient member so that the angle subtended bythe short and long legs is reduced as the lifting triangle approachesboth its most open and closed forms, as compared to the angle subtendedwhen there is no dynamic control. This dynamic excursion of theeffective termination point of the resilient member has the effect ofactively varying the effective spring rate of the resilient member, andthus providing predictably consistent lifting ability as thehitherto-unusable extremes of parallelogram excursion are approached.

Further, the cyclical action of the cams or crankshaft linkages isarranged to be a selectably fixed dimension, so the dynamic adjustmentof spring termination offset can be contoured more or less radically atthe same time as the general level of iso-elasticity is set. In contrastto previous methods of altering iso-elasticity, intended to provide anoverall harder or softer “ride”, the dynamic means of embodiments of theinvention additionally exaggerate the active increase and decrease oflift respectively as low and high positions of the lifting triangle areapproached. In practice, when the lifting triangle is incorporated intoa parallelogram support arm linkage, the effective center of the cam(s)or the pivot location of crankshaft(s) is conveniently referenced to andactuated by the top link as its angle parallels the ‘long’ leg of thelifting triangle throughout the excursion of the arm.

In a preferred embodiment of the present invention, the action of thecams or cranks can be plotted graphically as the degree of offset vs.the angular degree of arm excursion (±70 degrees from horizontal),resulting in generally parabolic curves.

Embodiments of the invention provide an adjustable iso-elastic supportarm for a camera stabilizing device which can make use of springs thatdo not have an appropriate rate (offset variably outside, as well asinside, the lifting triangle).

Embodiments of the invention also may provide an adjustable iso-elasticsupport arm for a camera stabilizing device which can actively providefor varying the contour of iso-elasticity established for the supportarm, substantially independently of the adjustment for supportingcameras of different weights.

Embodiments of the invention provide the features described in the twoparagraphs immediately above by including a support arm for the camerastabilizing device that comprises a parallelogram linkage that is biasedupward by a unitary, extendable and retractable resilient member, oneend of which may be selectably raised or lowered along a preferablycurved member mounted with respect to a pivot that is preferably commonwith a pivot of the parallelogram. The resilient member termination pathcan be additionally, arcuately adjusted, both fixedly and dynamically bya cam, crankshaft linkage, or the like, so that the resilient memberattachment point can be swung inwardly and outwardly with respect to avertical parallelogram side so as to dynamically alter the effectivelifting power of the resilient means. Irregular cam shapes are alsocontemplated and within the scope of the invention to more particularlycontour the lifting profile to produce appropriate arm performance.

DESCRIPTION OF THE DRAWINGS

For further detail regarding embodiments of the support arms produced inaccordance with the present invention, reference is made to the detaileddescription which is provided below, taken in conjunction with thefollowing illustrations.

FIGS. 1 a-b show a prior art support with three-spring arm sections.

FIG. 2 illustrates the mechanism of the prior art three-spring arm withadjustable spring termination.

FIG. 3 is a diagram of a force exerting device according to anillustrative embodiment of the invention.

FIG. 4 diagrammatically shows the lifting triangle ABC incorporatedwithin a parallelogram support linkage according to the prior art.

FIG. 5 diagrammatically defines DY and DX adjustments of the springtermination height and offset from vertical according to an illustrativeembodiment of the invention.

FIG. 6 diagrammatically illustrates the use of a cam with an offsetcenter and a cam follower to dynamically alter DX in response to motionof the parallelogram (proportionally with the height of DY) according toan illustrative embodiment of the invention.

FIG. 7 illustrates the cam of FIG. 6 with the addition of a variablevalue for DX according to an illustrative embodiment of the invention.

FIGS. 8 a-b diagram the substitution of a crank linkage (with its pivotoffset) to produce the effect of a circular cam to dynamically alter DXin response to motion of the parallelogram (also proportional to theheight of DY) according to an illustrative embodiment of the invention.

FIG. 9 diagrammatically illustrates the substitution of an adjustableturnbuckle for the fixed crankshaft according to an illustrativeembodiment of the invention.

FIGS. 10 a-b are partial isometric views of the mechanism of theillustrative embodiment of FIG. 9.

FIG. 11 is an exploded isometric assembly drawing of the mechanism of asingle complete arm segment of an illustrative embodiment of theinvention.

FIG. 12 is a cutaway side view of an arm segment of an illustrativeembodiment of the invention showing the vertical pivot attachments formounting the arm to an operator on the left and to a camera (or to asecond arm segment) on the right.

FIG. 13 is a solid side representation of a support arm according to anillustrative embodiment of the invention.

FIGS. 14 a-c provide three views of a chambered extrusion formed into aparallelogram support arm link according to an illustrative embodimentof the invention.

FIGS. 15 a-b depict three views of a chambered extrusion formed into aparallelogram support arm end block according to an illustrativeembodiment of the invention.

FIG. 16 plots Dx values (at three values of Dy) against a range ofangles Ø of parallelogram motion, from 20° to 160° and graphs theparabolic nature of Dx travel according to an illustrative embodiment ofthe invention.

FIG. 17 diagrams the results of a graphical solution, given the statedcrank link length and crank offset, for Dx, D, S, S1, H and P asdefined, and shows the formulas employed according to an illustrativeembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 a, 1 b and 2 illustrate a support apparatus of the prior art,which the inventor originally devised to obtain stabilized motionpicture film and video images and which was offered for sale under thetrademark “Steadicam®”. As illustrated, the support arm for theapparatus includes a pair of parallel upper arms links 102, 104, whichare pivotally coupled at one end to a connector hinge bracket 106. Theother ends of the upper arm links 102,104 are pivotally coupled to anupper arm medial hinge bracket 108. A second pair of parallel forearmlinks 110, 112 is pivotally coupled between a forearm medial bracket 114and a camera support bracket 116. A camera mounting pin 117 is providedin the camera support bracket 116.

The upper arm medial bracket 108 and the forearm medial bracket 114 arerotatably coupled together along one side by a hinge 118. The connectorhinge bracket 106 is rotatably coupled at its center to one end of alower support hinge plate 120. The other end of the lower support hingeplate 120 is rotatably coupled to a fixed support block 122 by a pin123. A spring 121, through which the pin 123 extends, biases the lowersupport hinge plate 120 in a clockwise direction.

One end of a tension spring 124 is coupled to the end of the upper armlink 102, which is pivotally coupled to the upper arm medial hingebracket 108. The other end of the tension spring 124 is coupled to oneend of the tension spring 126 by a section of cable 128 which rides onand around a pulley 130 which is rotatably coupled to the upper arm link102. The other end of the tension spring 126 is coupled to one end of atension spring 132 by a section of cable 134 which rides on and around apulley 136 which is rotatably coupled to the upper arm link 104. Theother end of the tension spring 132 is coupled to the end of the upperarm link 104 adjacent to the connector hinge bracket 106.

Similarly, one end of a tension spring 138 is coupled to the end of theforearm link 110 adjacent to the camera mounting bracket 116. The otherend of the tension spring 138 is coupled to a tension spring 140 by acable 142 which rides on and around a pulley 144 which is rotatablycoupled to the forearm link 110. The other end of the tension spring 140is coupled to one end of a tension spring 146 by a cable 148 which rideson and around a pulley 150 which is rotatably coupled to the forearmlink 112. The other end of the tension spring 146 is coupled to the endof the forearm link 112 adjacent to the forearm medial hinge bracket114.

A weight, such as a camera which is supported at the support bracket116, behaves as an object in free space beyond gravity since the upwardforces which the tension springs 124, 126, 132 and 138, 140, 146 exert,in effect, counteract gravity. The weight tends to travel in a straightline until influenced otherwise and tends to retain the same angle untilinfluenced otherwise. As a result, the upper arm links 102, 104 roughlycorrespond to the upper arm of the user and the forearm links 110, 112roughly correspond to the user's forearm, in terms of their threedimensional geometry, as the support arm is used either high, low, or toeither side.

FIG. 2 illustrates the present inventor's more recent prior art. Itshows a tensioning assembly 270 for implementing the requiredadjustments. To this end, a series of eight trunnions 271, 272 areschematically shown which define the bearing positions (the pivots) ofthe parallelogram structure of a support arm section (not shown forpurposes of clarity). An end of a first spring segment 273 is fixedlyconnected to the lower link of the arm section, at 274. The opposite endof the first spring segment 273 is serially connected, through a pulley275, with a second spring segment 276. The second spring segment 276 isserially connected, through an angled pulley 277, to a third springsegment 278. The third spring segment 278 terminates at a carrier block280, which constitutes the point of origin.

The carrier block 280 is received by a pin 281, which interfaces withthe carrier block 280 through a post 282. The eccentric pin 281 ispreferably offset (e.g., by 5°) from a line 283 which vertically bisectsa plane connecting the left-most trunnions 271. The carrier block 280 isdriven along (up and down) the eccentric pin 281 by a lead screw 284. Anadjustment knob 285 is provided to rotate the lead screw 284, andaccordingly, to linearly vary the effective height of the point oforigin of the tensioning assembly. Also provided is an adjustment knob286, for rotating a worm 287. The worm operates to rotate a worm gear288, which in turn operates to rotate the eccentric pin 281. Thisoperates to laterally displace the path defined for the carrier block280, suitably varying (displacing) the point of origin.

Embodiments of the invention permit equipoising of the load at far moreoblique and far more acute angles than previously possible. In anillustrative embodiment shown in FIG. 3, this is accomplished byproviding a force exerting device 300 having a load arm 302 pivotableabout a load pivot 312 and forming a first side of a force exertingstructure 328. Although the term “triangle” is often used herein, theactual shape of the force exerting structure can vary somewhat from atrue triangular form, for example because of connecting components thatmay protrude from the triangular form, various attachment points oradditional structural sides. A resilient member 314 having a first end316 attached to the load arm and a second end is attached to atermination point 318, which is displaced from the load pivot 312 andforms a second side of the force exerting triangle. A third side 320 ofthe force exerting triangle extends from the termination point 318 tothe load pivot 312. In this embodiment of the invention, the terminationpoint can be adjusted in more than one direction. In an exemplaryembodiment of the invention, a first adjustment mechanism moves thetermination point 318 to change the length of the third side 320 of theforce exerting triangle 328. A second adjustment mechanism moves thetermination point in a direction other than the direction produced bythe first adjustment. In an illustrative embodiment of the invention,the second adjustment direction is substantially perpendicular to thefirst adjustment direction. Examples of these two adjustment mechanismsare designated by Dx and Dy in FIGS. 5 and 7, although they need not beperpendicular as the “x” and “y” designations may imply. Optimum choiceof the two adjustments allows the termination point 318 location tocross a substantially plumb line 322 that passes through the load pivot312 as the load arm 302 pivots about the load pivot 312. This alters theequipoising contour throughout the pivotal excursion of the load arm ascompared to prior art mechanisms in which the termination point did notcross the plumb line. It is noted that a single adjustment may be usedto accomplish the same as two separate adjustment mechanisms.Additionally, a third adjustment mechanism can be included to move thetermination point outside the plane of movement created by the otheradjustment mechanism(s).

A turnbuckle or other threaded adjustment mechanism, may be used toproduce at least one of the adjustments. Other adjustment mechanisms arewithin the spirit and scope of the invention. The adjustment amounts maybe made in discrete increments or may span a continuous spectrum ofvalues.

Another illustrative embodiment may provide additional equipoisingability by having a force modification device 304 functionally connectedto the third triangle side 320 to produce dynamic movement of thetermination point 318 in response to motion of the load arm 302 aroundthe load pivot 312. The force modification device may be for example, acrankshaft or a cam. The force modification device causes the third side320 of the force exerting triangle to move toward and away from plumbline 322 as load arm 302 moves. The amount termination point 318 moves,and where within load arm 302's excursion it moves, is controlled by theshape and position of the center point of the cam. Movement of thetermination point in this manner puts it in different positions ascompared to the prior art and causes resilient member 314's length anddistribution of forces created by it to differ compared to the priorart, where the position of end 318 was not dynamically modified. Thesechanges created by the force modification device enable the inventivesupport arm to behave in a more desirable manner at the extremes of thearm's excursion as compared to prior art arms. Equipoising of the loadat far more oblique and far more acute angles is now possible.

It is noted that parts described as being “connected” to one another,include direct connections and indirect connections, such as where acoupling-type part or parts may be used.

As load arm 302 is swung through its excursion, such as upward ordownward, resilient member 314 expands or contracts thereby changing theforce it exerts at a particular rate. This rate can be modified by theforce modification device at particular points along the excursion ofload arm 302. The force modification device preferably decelerates thisrate of change at the extremes of excursion, namely toward or nearpositive and negative 90°, thereby smoothing out the motion by reducinglockup, lurching etc. In a particular embodiment of the invention, theforce modification device causes eccentric movement of the terminationpoint, such as by use of an irregularly shaped cam.

The force exerting device may include a pivotal parallelogram structurewherein load arm 302 is a side of the parallelogram. Two suchparallelograms can be pivotally connected to form a bendable orpivotable force exerting device. Non-parallelogram forms of the forceexerting device may also be linked together.

The force exerting device may also have an attachment mechanism toattach load arm 302 to a movable carrier for operation as a portabledevice.

The fixed adjustment mechanisms may be motorized and may be computercontrolled. The computer control system may include a program to controlone or more of the adjustments in response to sensed input. One or moreof the adjustment mechanisms may be manually controlled by a componentdisplaced from the arm, such as a foot peddle.

The first and second adjustments may be computer controlled.

The invention also includes a method of exerting forces on objects. Aforce exerting device such as described herein is provided. Thetermination point is adjusted to change the length of the third side ofthe force exerting triangle to change the lifting power of the forceexerting triangle. The termination point is further adjusted in adirection that is substantially perpendicular to the first adjustmentdirection so as the load arm pivots about the load pivot the terminationpoint location can cross a substantially plumb line passing through theload pivot to alter the equipoising contour over at least part of thepivotal excursion of the load arm. In a particular embodiment of theinvention, the method further includes adjusting the termination pointso that the first and second adjustments are proportional. In yetanother embodiment of the invention, the method further includesdynamically moving the termination point in response to motion of theload arm around the load pivot.

In further illustrative embodiments of the invention, the force exertingdevice has a dynamic termination point adjustment, but not necessarilythe initial set point adjustments because in some applications this maynot be necessary. For example, when the force exerting device is used ina particular product having a constant load, and to which no additionalloads will be attached, the initial set points can be factoryestablished, without the need for adjustment capabilities. Of course,one or more additional set point adjustment mechanisms can still bedesirable and are within the scope of the invention. Generally, theforce modification device will dynamically adjust the resilient membertermination point position with respect to a substantially plumb linethat passes through the load pivot based on motion of the load armthereby varying the resilient member's exerted force. The dynamicadjustment may be eccentric such as described above. Other featuresdescribed with respect to the embodiments having two initial terminationpoint adjustments can be used with the dynamic adjustment feature,whether or not the initial termination set point adjustments are used.

FIG. 4 diagrammatically shows two positions of the lifting triangle ABCincorporated within a parallelogram support linkage. Resilient member403 forms a side of the force-exerting triangle, which is here shown aslifting triangle ABC. Resilient member 403 is here shown, therefore as atension spring. In this illustration, side 401 is in both positionscontiguous with fixed side 405 and the spring attachment point 419 islocated on the line between point A and pivot 426. In order to exactlycounter a weight throughout the potential excursion of parallelogram402, 404, 405, 406 as shown, the tensioning assembly would require thespring rate specified by the formula K=P/Dy (where K=spring rate, P=loadand Dy=height of side 401. The tension spring would only fit within theavailable diagonal distance BC as shown if an impractically high springrate and an impractically low value for side 401 were employed.(example: If P=40 lbs a spring rate of 160 lbs/inch would exactlycounter P if the length of side 401 was 0.25″). If the length of side401 was increased, the weight of P would necessarily increaseproportionately to remain in equilibrium with the lifting force oftriangle ABC.

FIG. 5 diagrammatically illustrates an exemplary mechanism to adjustspring termination height and offset from side 505, and further diagramsa novel way to equipoise load P using a tensioning assembly of a ratethat is inappropriate according to the above formula K=P/Dy but isuseful for other reasons. The tensioning assembly may, for example, bespecified to fit within the diagonal space of a parallelogram withoutthe high spring rate and low aspect ratio that would otherwise be calledfor. If the termination point 519 of spring 503 is displaced outside ofthe adjacent, side 505 of the parallelogram formed by sides 502, 504,505 and 506, the lifting force becomes generally less efficient as theparallelogram is moved both upward and downward from the level attitudeshown, and which is known in the art to provide an approximation ofequipoise. Embodiments of the present invention introduce a mechanism toadjustably vary this offset in a manner that remains proportional to thechanging height of the lifting triangle. The path 518 of potentialspring termination points is angularly displaced from line 521, anextension of side 505, by means of Dx lead screw 514 which is adjustedby knob 516 to arcuately pivot side 501 (path 518) at pivot point A, andthus offset spring termination point 519 with respect to side 505, whichis here shown to be vertical. In addition, Dy adjusting knob 515 turnslead screw 513 to raise and lower spring termination point 519 alongspring termination path 518 in order to increase or decrease the liftingforce of the triangle ABC.

FIG. 6 diagrammatically illustrates an illustrative embodiment of theinvention which introduces the use of a generally circular cam 622 andcam follower 623 to further equalize the force of the lifting triangleso that it may more closely equipoise the load at all values of angle Ø.To accomplish this, cam 622 is fixed to link side 606 with its center617 offset from the fixed point and cam follower 623 is fixed to block611. Block 611 is fixed to bearing shaft 609 which is adjustably fixedto spring carrier 612 by lead screw 613 in a manner to pivot with block610 around point A so as to dynamically alter the momentary Dx offset624 in response to excursion of the parallelogram (proportionally withthe height of spring termination 619). (The line between 619 and point Adefines side 601 of the lifting triangle, which is also the Dydistance.) The cyclical motion of the cam follower 623 in response tothe excursion of the parallelogram (of sides 602, 604, 605, 606) fromØ20° up to 160° provides a series of Dx offsets that, if plotted againstthese angles is generally parabolic. (See FIG. 16 and FIG. 17 fordiagrammatic and formulaic descriptions of this aspect of embodiments ofthe invention.) The larger the distance between the parallelogram pivot626 and the cam center 617, and the smaller the general radius of thecam shape, the steeper the plotted parabola, and therefore the moreradical the cam effect on Dx offset 624 as the parallelogram approachesthe high and low positions of the angle Ø which may be as great as from20° to 70°, which have hitherto been virtually uncontrollable withrespect to predictably equipoising load P. It is noted that although thearm is shown in the figures with the resilient member above the arm, theentire apparatus can be inverted.

FIG. 7 illustrates another embodiment of the present invention that addsto the effect of cam 622 of FIG. 6, a variable value for Dx (the effectof which is preferably proportional to the height of Dy). Dx adjustingknob 716 turns Dx lead screw 714 to adjustably position cam follower 623with reference to bearing shaft 609 and thus set the value of offset 624of spring termination 619, which is also momentarily incremented ordecremented by the action of cam 622 driven by the excursion of side 606of the parallelogram in angle Ø.

Embodiments of the invention control the behavior of the arm at high/lowextremes (such as ±70°) so that typical problems such as lurching overcenters and locking up may be solved by simply shortening the cranklength. This simultaneously reduces the offset and increases theradicality of the cam effect to reduce Dx as the arm approaches ±70°.

FIG. 8 a diagrams another illustrative embodiment of the presentinvention which, substitutes for the cam of FIGS. 6 and 7, a cranklinkage 825 with its wrist pin pivot 817 fixedly offset on an extensionof link 806, at distance 20 from link pivot 826. Movement ofparallelogram link 806 around pivot 826 between high and low values ofangle Ø moves crank pivot 817 through arcuate path 828, and thus crank825, acting through outboard crank pivot 823, moves block 811 to producean effect similar to that of the circular cam and follower of FIGS. 6and 7 and likewise dynamically alters the Dx offset of springtermination 819 with respect to 821 in response to the excursion of theparallelogram. As with the cam configuration, the motion created by thecrank linkage can be eccentric. Note that this alteration is likewisearcuate around pivot point A and is proportional to the height of side801 (Dy). In the preferred embodiment illustrated, note that springtermination path 818 does not pass through point A. Spring terminationpath 818 crosses over line 821 at crossover point 827. This providesthat as Dy distance 1 is reduced by means of lead screw 813, the nominalDx values will become negative before Dy is zero, at roughly the pointthat the chosen spring rate would have equipoised a diminished load Paccording to the above-stated formula (K=P/Dy). The higher the springrate, the more the offset varies toward the ‘outside’ of the plumb linethat is approximated by the substantially vertical leg of theparallelogram linkage.

FIG. 8 b shows a closer detail of the illustrative embodiment of FIG. 8a, illustrating that captive nut 829 within top bearing block 811 fixeslead screw 813 longitudinally so that it may adjust the position ofcarrier 812 and its enclosed bearing along lead screw 813. Dx offsetdistance 824 is momentarily altered by the circular excursion of pivot817 through path 828 around pivot 826 as the position of link 806 movesbetween low and high values of angle Ø and actively causes crank 825 topivotally vary the angle of bearing shaft 809 about point A. Theresulting momentary variation in offset 824 is also proportional to theadjustably fixed height of side 1 (Dy).

FIG. 9 diagrammatically illustrates an embodiment of the presentinvention, in which the crank of FIGS. 8 a-b is replaced by a turnbuckleassembly of variable length. Shortening the turnbuckle 932, has atwofold effect: it reduces the Dx value and at the same time causes thecam effect of the crank linkage comprising the turnbuckle 932 to becomemore radical at the high and low extremes of angular motion of theparallelogram in angle Ø. In another embodiment of the invention,fixedly raising or lowering the turnbuckle link pivot 917 with respectto the centerline of link 906 produces offset distance 933 between pivot917 and the center line of link 906 that respectively causes the ‘cam’effect to be more or less radical as Ø decreases and increases. Forexample, lowering the pivot 917 produces a negative offset distance 933that decreases the ‘cam’ effect as Ø decreases and vice versa. Length931 of crank linkage 925 controls offset Dx (w/respect to line 921).Increasing the length creates a more oblique lifting triangle, whileshortening the length causes it to be less oblique. It is noted thatother threaded adjustment mechanisms are within the spirit and scope ofthe invention.

FIG. 10 a is a partial isometric view of the mechanism of the preferredembodiment of FIG. 9, illustrating the spatial positions of the trunnionscrews 34 that define the parallelogram pivot positions. Spring 3 withterminal 35 and associated hardware terminates at pivot 19 on carrier 12which rides up and down linear bearing shaft 9 in response to adjustmentof lead screw 13 by knob 15. Turnbuckle assembly 32 is expanded orcollapsed by knob 16 which draws pivots 17 and 23 together or apart andperforms the function diagrammed in FIG. 9 to pivot bottom bearing block10 and arcuately adjust point 19 in response to the excursion of theparallelogram link 6 (not shown), and proportionate to the height ofcarrier 12. Note that the turnbuckle assembly 32 provides for the pivotsto be closer together than possible with conventional turnbuckles andthe adjusting knob 16 can be displaced away from the line between thepivots 17 and 23, and thus out of the way of the end block (not shown)as employed in embodiments of the invention.

FIG. 10 b is an alternative angle of an isometric view of the mechanismof FIG. 10 a showing the use of a loop end spring 3 extending from axle36 to spring link 37 which in turn is pivotally linked to carrier 12which contains linear bearing 9 a. This view more clearly shows topbearing block 11 which forms the upper attachment of linear bearingshaft 9, and also illustrates the approximate centerline 47 of pivot 17for turnbuckle assembly 32.

FIG. 11 is an exploded isometric assembly drawing of the mechanism of asingle complete arm segment of the preferred embodiment of the presentinvention, which illustrates the components of the Dx/Dy adjusting anddynamically moving assembly. End block 58 is pivotally attached to links52 a and 56 a. Link 56 a provides attachment to pivot 54 which engagesthe turnbuckle assembly 60. Bottom bearing block 62 engages bearingshaft 59. Carrier 64 encloses bearing 59 a and is driven along shaft 59by lead screw 66, which is longitudinally fixed within top bearing block68 by captive nut 70 and which is turned by knob 72. End block 57completes a parallelogram.

FIG. 12 is a cutaway side view of a single arm segment of a preferredembodiment of the invention showing the pivot locations for mounting thearm segment to a supporting body and payload via end blocks 80 and 82,respectively, if the arm is deployed in the attitude shown, and to endblocks 82 and 80, respectively, if the arm is deployed inverted (notshown) which is an equally valid configuration. Note that a second armsegment can optionally be included, via a hinge (not shown), between oneof the end blocks and either the support body or camera (neither isshown) as appropriate. (see FIG. 15)

FIG. 13 is a solid side representation of the complete, two-segmentsupport arm of a preferred embodiment of the present invention. Supportbody (not shown) mounting hardware 98 is pivotally attached to ‘upper’arm segment 90, which is pivotally attached via hinge 92 to ‘forearm’segment 94, which is adapted for connection to the payload (such as acamera) using post 96. Note that if the arm were inverted, post 96 andbody mounting hardware 98 could simply be interchanged and the arm wouldlift appropriately.

FIG. 14 a-c display three views of a chambered extrusion formed intoparallelogram support arm links to provide a light, torsionally rigidmember. FIG. 14 a is a perspective view and shows a solid outer surface,however, openings can exist on the surface. FIG. 14 c shows an end viewof the extruded chambers, which are roughly triangular in section inthis embodiment, and which run the length of the parallelogram link asshown in the isometric view of FIG. 14 b.

FIGS. 15 a-b show views of a chambered extrusion formed into theparallelogram end blocks of an illustrative embodiment. FIG. 15 b showsa top view of the end block having chambered voids 20, which providelightweight and torsional stiffness. The isometric view in FIG. 15 aillustrates the extrusion formed into one of the end blocks of thepreferred embodiment, yet does not display any of voids 20.

FIG. 16 plots Dx values (at three values of Dy) against a range ofangles Ø of parallelogram motion, from 20° to 160° and graphs theparabolic nature of Dx travel when Dx is varied by the crank linkage ofthe support arm embodiment of FIGS. 8 and 9.

The desired force exerting device specifications will depend at least inpart on the materials and components used and the load supported by thedevice. These parameters must be balanced with various specificationssuch as cam shapes, crank axle offsets, crank lengths, spring rates andload lengths for optimum equipoised motion.

FIG. 17 diagrams the results of a graphical solution based on thefollowing formulas:DX=³¹ 0.95(α)²+0.332(α)−0.156   1)D=SQRT[(DX)²+(DY)²]  2)S=SQRT[(l sin α+DX)²+(l cos α+DY)²]  3)S1=(l ² −D ² +S ²)/2S  4)H=SQRT[l ²−(S1)²]  5)If ΣM _(a)=0, P=((F)(H)−(W/2) l sin α)/l sin α  6)

-   Wherein-   P: Payload-   DX, DY: Define a location for spring attachment-   S: is the extended spring length-   H: is a line perpendicular to S-   α: is the arm angle-   F: is the spring force=κ(Δs)+Initial Force-   M: moment about point a.

The parabolic function as described above produces regular lift. Thecrank effectively applies a reverse parabolic function to linearize it.Therefore, if a zero offset is selected, the ‘ride’ will be hard andnon-iso-elastic. (at ±70° with no offset one must lift 10 lbs or pushdown with 8). With appropriate offset and ‘geo’ curve mere ouncessuffice at both ends with a single high-rate spring that fits into thediagonal of the lifting triangle.

If a nominally appropriate offset position is selected but no ‘cam’effect is used, the ride will be softer, but as nominal Dx increases, atsome point the arm lifting force will be excessive at the top andinsufficient at the bottom of range and the arm will be impelled overcenters at both the top and bottom. At this time the lifting curve willfavor a point just above center so the arm will leap up to that‘spring-level’ point and be sluggish for the next 30 degrees upward andthen will accelerate toward lockup:

According to illustrative embodiments of the invention, the arm's liftcan be reduced to zero and indeed sent into the negative (pushing down)by motorizing the Dy lead screw, in order, for example, to facilitatethe use of an ultrasound transducer without the need for the operator tosupply the downward force. Dx and dynamic adjustments can also bemotorized. The Dx lead screw (or turnbuckle) can also be motorized. BothDy and Dx can be dynamically controlled by a manual means (such as afoot pedal) or by computer, in response to outside stimuli, includingthe ‘feel’ to the accompanying hand, or a screen reference, such as theimage on an ultrasound display screen. Each of Dy and Dx may becontrolled in discrete increments or in a continuous manner.

While the invention has been described by illustrative embodiments,additional advantages and modifications will occur to those skilled inthe art. Therefore, the invention in its broader aspects is not limitedto specific details shown and described herein. Modifications, forexample, to the materials, specific components and their layout, may bemade without departing from the spirit and scope of the invention.Accordingly, it is intended that the invention not be limited to thespecific illustrative embodiments, but be interpreted within the fullspirit and scope of the appended claims and their equivalents.

1. A force exerting device comprising: a load arm pivotable about a loadpivot and forming a first side of a force exerting structure; aresilient member having a first end attached to the load arm and asecond end attached to a termination point displaced from the load pivotand forming a second side of the force exerting structure; a forceexerting structure third side extending from the termination point tothe load pivot; a first adjustment mechanism to move the terminationpoint to change the length of the third side of the force exertingstructure; a second adjustment mechanism to move the termination pointin a direction other than the direction produced by the first adjustmentmechanism, wherein the combination of the two adjustments allows thetermination point location to be set on either side of a plumb linepassing through the load pivot; and wherein at least one side of theforce exerting structure is chambered.
 2. The force exerting device ofclaim 1 comprising a threaded adjustment mechanism to produce at leastone of the adjustments.
 3. The force exerting device of claim 1 furthercomprising a pivotal parallelogram wherein the load arm is a side of theparallelogram.
 4. The force exerting device of claim 1 furthercomprising an attachment mechanism to attach the load arm to a movablecarrier for operation as a portable device.
 5. The force exerting deviceof claim 4 further comprising the movable carrier attached to the loadarm.
 6. The force exerting device of claim 1 wherein one or more of theadjustment mechanisms is motorized.
 7. The force exerting device ofclaim 1 wherein one or more of the adjustment mechanisms is manuallycontrolled by a component displaced from the arm.
 8. The force exertingdevice of claim 1 wherein the first and second adjustments areproportional.
 9. The force exerting device of claim 1 further comprisinga second force exerting device pivotally connected to the first forceexerting device.
 10. A force exerting device comprising: a load armpivotable about a load pivot and forming a first side of a forceexerting structure; a resilient member having a first end attached tothe load arm and a second end attached to a termination point displacedfrom the load pivot and forming a second side of the force exertingstructure; a force exerting structure third side extending from thetermination point to the load pivot; a first adjustment mechanism tomove the termination point to change the length of the third side of theforce exerting structure; a second adjustment mechanism to move thetermination point in a direction other than the direction produced bythe first adjustment mechanism, wherein the combination of the twoadjustments allows the termination point location to be set on eitherside of a plumb line passing through the load pivot; and wherein one ormore of the adjustment mechanisms is motorized.
 11. The force exertingdevice of claim 10 wherein one or more of the adjustment mechanisms iscomputer controlled.
 12. A force exerting device comprising: a load armpivotable about a load pivot and forming a first side of a forceexerting structure; a resilient member having a first end attached tothe load arm and a second end attached to a termination point displacedfrom the load pivot and forming a second side of the force exertingstructure; a force exerting structure third side extending from thetermination point to the load pivot; a first adjustment mechanism tomove the termination point to change the length of the third side of theforce exerting structure; a second adjustment mechanism to move thetermination point in a direction other than the direction produced bythe first adjustment mechanism, wherein the combination of the twoadjustments allows the termination point location to be set on eitherside of a plumb line passing through the load pivot; wherein one or moreof the adjustment mechanisms is computer controlled.
 13. The forceexerting device of claim 12 further comprising a computer programmed tocontrol one or more of the adjustments in response to sensed input. 14.A force exerting device comprising: a load arm pivotable about a loadpivot and forming a first side of a force exerting structure; aresilient member having a first end attached to the load arm and asecond end attached to a termination point displaced from the load pivotand forming a second side of the force exerting structure; a forceexerting structure third side extending from the termination point tothe load pivot; a first adjustment mechanism to move the terminationpoint to change the length of the third side of the force exertingstructure; a second adjustment mechanism to move the termination pointin a direction other than the direction produced by the first adjustmentmechanism, wherein the combination of the two adjustments allows thetermination point location to be set on either side of a plumb linepassing through the load pivot; and wherein one or more of theadjustment mechanisms is manually controlled by a component displacedfrom the arm.
 15. The force exerting device of claim 14 wherein thecontrol component is a foot pedal.
 16. A method of exerting forces onequipment comprising: providing a force exerting device having: a loadarm pivotable about a load pivot and forming a first side of a forceexerting structure; a resilient member having a first end attached tothe load arm and a second end attached to a termination point displacedfrom the load pivot and forming a second side of the force exertingstructure; a third force exerting structure side extending from thetermination point to the load pivot; making a first adjustment of thetermination point using a first adjustment mechanism to change thelength of the third side of the force exerting structure to change thelifting power of the force exerting structure; making a secondadjustment of the termination point in a direction other than thedirection produced by the first adjustment mechanism using a secondadjustment mechanism, wherein the combination of the two adjustmentsallows the termination point location to be set on either side of aplumb line to alter the equipoising contour over at least part of thepivotal excursion of the load arm. wherein the first and secondadjustments are dynamically made by moving the termination point inresponse to motion of the load arm around the load pivot.
 17. The methodof claim 16 further comprising: adjusting the termination point so thatthe first and second adjustments are proportional.